Did Ocean Water Originate From Comets?

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A family of comets from the Kuiper Belt may have assisted
asteroids with bringing water to early Earth, a key development
in the planet's ability to host life.

Scientists believe Earth’s water was delivered sometime after the
planet formed, as its close proximity to the sun would have
boiled off water inside rocks that were part of the original
building materials.

Previous studies of meteorites, which are bits of asteroids that
land on Earth, show a water chemistry that is similar to Earth’s
oceans. The analysis is based on the ratio of regular water --
two hydrogen atoms bound with an oxygen atom, or H2O -- and
so-called “heavy water,” which has an extra neutron in its
nucleus.

The target, Comet Hartley 2, is believed to have formed in the
Kuiper Belt region, located beyond Neptune's orbit. Hartley 2 is
now a member of the Jupiter family of short-period comets that
swing around the sun in less than 20 years. The comet's water
chemistry matches that of Earth's.

"This is an important constraint on models of the formation of
planets in the solar system, a field of science which is moving
forward very rapidly at present," astronomer Miriam Rengel of the
Max Planck Institute for Solar System Research in Germany, wrote
in an email to Discovery News.

Previous studies, which looked at comets originating from the
Oort cloud, a spherical cluster of icy bodies in the outer solar
system, led scientists to conclude that only about 10 percent of
Earth's water could have come from comets.

The finding significantly boosts the pool of resources available
to carry water to Earth.

"The reservoir of material that has the same isotopic signature
as the Earth’s water is much larger in our solar system than we
had previously assumed," astronomer Ted Bergin, with the
University of Michigan, told Discovery News.

The studies were made in October and November 2010 as Hartley 2
passed closely by Earth with the European Space Agency's Herschel
space telescope. The research is reported in this week's
Nature.